High-voltage discharge device



Oct. 22, 194%. c. M. sLAck El'AL 2,409,716

7 HIGH VOLTAGE DISCHARGE DEVICE I I Filed. Sept. 27, 1 941 2Sheets-Sheet l I I aNvENToRs v C. mnsg cvr A. E'A'lF/CE 0ct.-22, 1946.c. M. SLACK ETAL HIGH VOLTAGE DISCHARGE DEVICE Filed Sept. 27, 1941 2Sheets-Sheet 2 INVENTORS M 146K ATTORNEY Patented Oct. 22; 19462,409,716 HIGH-VOLTAGE DISCHARGE DEVICE Charles M. Slack, Glen Ridge,Louis F. Ehrke, Newark, and Clarence E. Dawley, Bloomfield, N. J.,assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application September 27, 1941, Serial No.412,566

8 Claims. 1

The present invention relates to discharge devices and more particularlyto high vacuum devices capable of passing high currents and capable ofwithstanding comparatively high voltage.

Devices of a somewhat similar nature are known to the art but in mostinstances they depend for their operation on the continual presence of ametallic vapor or gaseous environment to carry current between theelectrodes. This limits the amount of current which can be passed by thedevice without the occurrence of destructive discharges.

It is accordingly an object of the present invention to provide adischarge device capable of passing high currents of the magnitude ofhundreds or even thousands of amperes.

Another object of the present invention is the provision of dischargedevices capable of passing exceptionally high currents at comparativelyhigh voltages wherein cold electrodes are employed between which thecurrent flows during operation of the device.

Another object of the present invention is the provision of a dischargedevice which passes exceptionally high currents by using field emissionfrom cold electrodes to initiate and sustain a discharge therebetween.

A further object of the present invention is the provision of adischarge device which passes exceptionally high currents by utilizingfield emission from cold electrodes to initiate and sustain a dischargetherebetween and wherein initiation of the discharge is controlled atwill.

Still further objects of the present invention will become obvious tothose skilled in the art by reference to the accompanying drawingswherein:

Fig. 1 is a side viewof a high vacuum discharge device constructed inaccordance with the present invention and showing schematically itsconnection to a load and a control circuit therefor.

Fig. 2 is a fragmentary sectional view onan en larged scale of theelectrode construction of the discharge device as shown in Fig. 1;

Fig. 3 is a sectional view taken, on the line III-III of Fig. 2;

Fig. 4 shows a modification which the electrode structure for thedischarge device of Fig. 1 may take;

Fig. 5 is a side view of a high vacuum discharge device showing amodification of the electrode 2 Fig. 6, of additional modificationswhich the electrode structure may take;

Fig. 10 is a fragmentary view of a further modification which theelectrode structure of the device as shown in Figs. 1 and 5 may take.

Fig. 11 is a sectional view taken on the line XI-XI of Fig. 10, and

Figs. 12 and 13 are each still further modifications which the electrodestructure for the high vacuum discharge device as shown in Fig. 1 maytake.

Referring now to the drawings in detail, a discharge device is shown inFig. 1 which comprises a vitreous envelope 5 provided with a pair ofelectrodes constituting an anode 6 and two-part cathode I and 8 as willbe hereinafterdescribed. The anode 6 is supported by a leading-inconductor 9 sealed through a reentrant press in provided at one end ofthe envelope 5, and in a similar manner a leading-in conductor I2 issealed through'a reentrant press I3 in the opposite end of the envelope.The inner end of the leading-in conductor I2 is shown provided with asuitable insulator M to the latter of which is also secured a furtherleading-in conductor l5 hermetically sealed to a side-arm [6 of theenvelope 5.

A conductor [8 is welded or otherwise affixed to the conductor l2 so asto constitute an extension of the latter to complete an electricalconnection to the cathode member 1 and similarly a conductor I9 issecured to the leading-in conductor l5 and completes an electricalconnection to the remaining cathode member 8. By reference now moreparticularly to Figs. 2 and 3, it will be noted that the anode 6 andmain cathode member I are metallic cylinders, which may beof tantalum,molybdenum, or an alloy known under the trade name of Kovar, closed attheir closely spaced adjacent ends except that the cathode member I isprovided with a small opening 20. The remaining metallic cathode member8 being of rod-like configuration has its end projecting through thissmall opening 20, thus leaving a very small spacing between the metallicrod-like member 8 and the surrounding edge of the cylindrical cathodemember 1 formed by the slightly larger diameter opening.- i l i l When apositive impulse of several thousand volts is applied to the cathodemember 8, field emission of electrons occurs from the edges of thesurrounding cathode member 1 due to thehigh potential gradient at thecathode. This field emis:

sion of electrons resulting from the high electrostatic field causes aminute arc to form at points around the edge of the cathode member Iapparently due to evolved metal vapor from this cathode member much inthe same manner that a cathode spot is formed on the surface of themercury cathode of a vapor electric discharge device. The positive ionbombardment resulting from ionization of the evolved metal vapor causedby the arc, heats this cathode member 7 or the metallic arc becomes anelectron source and the impedance of the device is so reduced that anelectron discharge is almost instantaneously initiated or transferredbetween the closely spaced cathode and anode. An electron-emissivecathode of enormous current capacity is accordingly provided despite thefact that the cathode is what is known in the art as a cold electrode.

In the fabrication of the discharge device of the present invention theelectrodes and all metal parts are thoroughly degasified and theenvelope preferably evacuated to a very high degree so that satisfactoryoperation of the device is entirely independent of vapor present in thetube. Satisfactory operation also results, however, with a metal vaporsuch as mercury present in the device so long as its pressure is suchthat the spacing between the cathode members is less (and preferablymany times less) than the mean free path of electrons in the vapor sothat firing or ignition of the device to form the metallic arc isentirely independent of the mercury vapor present. The same conditionholds respecting the ensuing electron discharge between the cathode andanode, for again the spacing therebetween is less than the mean freepath of electrons in the mercury vapor at the pressure employed, so thatthis electron discharge is also independent of the mercury vapor presentand apparently supported entirely by the metal vapor ionization producedby the field emission are. The presence of mercury vapor in the deviceperforms the function of making the high current discharge more certainand increases the area of the anode impinged by the electrons from thecathode.

In order to obtain a discharge in the device particularly at will, it isdesirable to keep the potential gradient at all electrodes as low aspossible due to the high voltage between the anode 6 and cathode 1 toprevent the occurrence of spurious discharges. At the same time thepotential gradient at the cathode 1 should be as high as possible due tothe voltage between the cathode members 1 and 8. Due to the positioningof the cathode member 8 in closer proximity to the cathode member 1 thanthe spacing between the anode 6- and cathode 18 the potential gradientat all the electrodes is thus properly selected. Also, to have lowenergy dissipated within the tube, it is necessary that the are spreadas quickly as possible between the anode 6 and cathode 18 and hence thisspacing should be kept as small as is consistent with the voltagetherebetween which is to be controlled.

Naturally these spacings between the electrodes will vary depending uponthe magnitude of the voltage to be controlled and existing between theelectrodes 6 and l, as well as the controlling voltage applied to thecathode member 8 to initiate the metallic arc discharge. However, as anexample, with an applied voltage of 20,000 volts to be controlledbetween the anode 6 and cathode l and with spacing of .2 cm., adischarge is satisfactorily and rapidly initiated by applying acontrolling voltage of 10,000 volts to the cathode member 8 with aspacing of .01 cm. between the latter and the adjacent cathode member 1.

From the above description it can thus be readily seen that thedischarge device of the present invention can be controlled at will tosupply enormous current to a load. A simple circuit for supplying suchcurrents to a load and for controlling a discharge is shown in Fig. 1.In this figure a condenser 22 of about .04 mfd. capacity is charged toabout 20,000 volts through a rectifying valve 23 from the secondarywinding 24 of a high voltage transformer 25, one plate of the condenser22 being grounded as at 26 and one end of the secondary winding 24 beingalso grounded at 2l', thus completing the charging circuit for thecondenser. The discharge circuit for the condenser 22 includes the highvacuum discharge device 5 having its cathode member I connected by aconductor 28 and leading-in conductor l2, [8 to one plate of thecondenser, while the remaining plate of the condenser 22 is connectedthrough a load 29 to the anode 5 of the discharge device by means ofleading-in conductor 9.

A high potential is accordingly impressed across the electrodes 6 and i,but since the electrodes are non-thermionic or cold electrodes nodischarge occurs in the device and hence the load 29 receives no energy.When it is desired to energize the load 29, a high voltage is impressedacross the cathode members I and 8 to cause the formation of an annulararc discharge at points around the edge of the cathode at the opening 20and having an annular appearance which initiates almost instantaneouslya thermionic discharge between the cathode 'l and anode E, as beforenoted.

The control circuit as shown in Fig. 1 comprises a high tensiontransformer 32 having its primary winding 33 connected to a suitablesource of supply of the customary domestic potential in the same manneras the primary winding of the transformer 25. The secondary winding 34of the transformer 32 is arranged to form a charging circuit for acondenser 35 by having one of its ends connected to ground as at 2'!with its other end connected to one plate of the condenser 35 through arectifying valve 36, and the charging circuit being completed bygrounding the remaining plate of the condenser 35.

The discharge circuit for this condenser 35 ineludes the primary winding37 of a high tension transformer 38, the secondary winding 39 of whichis connected to the cathode members I and 8 so as to impress a highvoltage'thereacross when it is desired to energize the load 29. In orderto control discharging of the condenser 35 a control tube 40 of theusual three electrode type is interposed between the condenser 35 andprimary winding 31. A voltage is impressed across the grid and cathodeelectrodes of this control tube 40 from a suitable source, such as abattery 42, and through a resistance 43 and normally closed switch 44,so that the polarity of the grid electrode is made highly negative withrespect to the cathode, in the usual manner of controlling a dischargethrough tubes of this type.

When it is desired to energize the load 2e, switches (not shown) arefirst closed which connect the primary windings of both transformers 25and 33 to a source of the customary domestic potential. This accordinglycauses the condensers 22 and 35 to accumulate a high voltage charge fromtheir respective charging circuits. as previously described. The switch-44 is then opened (either manually by an operatoror automatically by arelay) which thus removes the negative charge supplied by the batteries42 to the grid of the control tube 45, allowing the charge to leak offthrough aresistance 45.

The condenser 35 will accordingly discharge through tube 4!] and primarywinding 31 of the high potential-transformer 38, thus inducing a highvoltage current in the secondary winding 39 which is impressed acrossthe cathode members 1 and 8. This, as before noted, causes the formationof an are at points around the edge of the opening 2!] of the cathodemember 1, making the latter a highemissive cathode which causes adischarge of enormous current from the condenser 22 across the cathode 1and anode 6 to the load 29, the magnitude of which is dependent upon thevoltage and load.

In addition to the embodiment of the electrode structure thus fardescribed, many other designs of the cathode are possible. For example,substantially the same design may be resorted to as shown in Figs. 1 to3, but the Side arm for the starting electrode eliminated by resortingto an arrangement such as shown in Fig. 4 wherein the leading-inconductors for the anode 6 and cathode member 1 are brought in from oneend of the tube while the cathode member 8 is supported from theopposite end of the envelope. Also, the cathode member 8 may extendthrough an opening 52 provided in the anode 6 of the same diamrod-likeanodes 69, all connected in electrical eter as the opening in thecathode member 7, 4

which thus permits either the electrode 6 or I to operate as anode orcathode.

In addition, the electrodes may comprise a plurality of rods with theirupper ends supported by an insulator 53, as shown in Figs. 5 and 6, orthe cathode member made of triangular form as shown at 54 in Fig. 7 andpositioned between two parallel connected rod-like anodes 55 and 56 withthe apex of the cathode member 54 spaced closely to the remainingcathode Inember51. A still further modification may comprise making thecathode member 58 and cathode member 59 of triangular shape and the twoanodes 60 and 52 substantially of pyramidal shape as shown in Fig. 8.Again, however, the electrodes 54 and 51, as well as the electrodes 58and 59 of each modification, may operate as starting electrode andcathode.

The modification as shown in Figv 9 differs from those previouslydescribed in that, while all of the electrodes are of trapezoidalconfiguration, they are of a material such as carbon supported uponmetallic leading-in conductors 63 with one cathode member being providedwith a metallic insert 54 of tungsten, tantalum, molybdenum or the like,from which the aforementioned are discharge is initiated by theremaining closely adjacent cathode member.

For the purpose of prolongin the useful life of the high power device ofthe present invention, a structure such as shown in Fig. 10 may beemployed. In this particular modification the oathode electrode 65 isshown as formed of a solid metallic cylinder provided with an annularflange 55 about its end periphery which is closely positioned adjacentthe closed end of the remaining disc-shaped metallic cathode member 6'].This construction provides a much greater edge surface for theinitiation of the arc discharge due to the concentration of theelectrostatic field about the two sharp annular edges formed by theperiphery of the flange 65, and following initiation of the arcdischarge the main high current discharge occurs between the cathode 65and the surrounding cylindrical anode 68.

This same feature of providing a, plurality of parallel, extend throughseparate openings 15 provided between the metallic cathode member H andremaining cathode member 12, as shown in Fig. 12. In Fig. 13 the cathodemember 13 and anode 14 are each formed of two rectangular metallicblocks with each pair again connected in electrical parallel and sodisposed that one corner of each block is positioned adjacent theremainin cathode member 75, thus again providing a plurality of sharpedges from which the starting arc discharge is initiated.

-' I It will thus become obvious to those skilled in the art that ahighvoltage discharge device is herein provided in which enormous currentsare passed by the tube by utilizing field emission of electrons from acold electrode to initiate a discharge. Moreover, operation of the tubecan be controlled at will and since the molecules necessary for ionformation are obtained from the cold electrodes themselves, a greatlyreduced deionization time results, thus enabling the device to be usedat much higher frequencies than is possible with gas or metallic vapordevices. Owing to the fact that the device of the present invention isnot subject to electron emission limitations, it can not only beemployed in applications where gas or vapor devices are now employed,but because of its advantages it can be used where these latter typedevices cannot be used owing to their inherent emission limitations.

Although several embodiments of the present invention have been'shownand described, it is to be understood that still further modificationsthereof may be made without departing from the spirit and scope of theappended claims.

We claim: a

1. A discharge device for passing high currents comprising an envelope,an anode and a cathode in said envelope and spaced in such closeproximity to each other that electron flow from said cathode is underthe influence of a strong electrostatic field, and said cathodecomprising a pair of members spaced closer to each other than eithermember to said anode to cause field emission of electrons from one ofsaid cathode members and the formation of a metallic arc dischargebetween said pair of cathode members with the evolution ofa metal vaporfrom one of said members, to reduce the impedance of said device andinitiate afield emission electron discharge between said cathode andanode accompaniedby enormous current fiow upon the appli cation of ahigh potential between said cathode members.

2. A discharge device for passing high currents comprising an envelope,an anode and a solid metallic cathode in said envelope and spaced insuch close proximity to each other that electron flow from said cathodeis under the influence of a strong electrostatic field, and said cathodecomprising a member provided with an edge of sharpened contour forconcentrating th electrostatic field thereat, and a second cathodemember spaced in closer proximity to the sharpened edge of saidfirst-mentioned cathode member than is said anode to cause fieldemission of electrons from said first-mentioned cathode member and theformation of a metallic arc discharge between said cathode members withthe evolution of a metallic vapor from one of said members,

for initiating a field emission electron discharge accompanied byenormous current flow between said cathode and anode upon theapplication of a high potential across said cathode members.

3. A discharge device for passing high currents comprising an envelope,an anode and a solid cathode insaid envelope and spaced in such closeproximity to each other that a high potential gradient is produced atsaid cathode and electron fiow from said cathode is under the influenceof a strong electrostatic field, said cathode comprising a member havinga surface of small radii of curvature for concentrating theelectrostatic field thereat, and a solid metallic member spaced incloser proln'mity to the sharp edge of said cathode member than is saidanode to produce a high potential gradient at said cathode surface andthe formation of a field emission arc discharge between said cathodemembers with the evolution of a metallic vapor from one of said members,for initiating a field emission electron discharge accompanied byenormous current flow between said cathode and anode upon theapplication of a high potential across said cathode members.

4. A discharge device for passing high currents comprising an envelope,an anode and a solid metallic cathode in said envelope and spaced insuch close proximity to each other that a high potential gradient isproduced at said cathode and electron flow from said cathode is underthe influence of a strong electrostatic field, said cathode comprising amember provided with a plurality of sharp edges for concentrating theelectrostatic field thereat and a second solid metallic memberpositioned adjacent the sharp edges of said first-mentioned cathodemember in closer proximity thereto than is said anode to produce a highpotential gradient at said cathode with field emission of electrons fromthe latter and the evolution of a metal vapor from one of said cathodemembers causing the formation of a metallic arc discharge between saidcathode members, for initiating a field emission electron dischargeaccompanied by enormous current flow between said cathode and anode uponthe application of a high potential across said cathode members.

5. A discharge device for passing high currents comprising an envelope,an anode and a cathode in said envelope and spaced in such closeproximity to each other that a high potential gradient is produced atsaid cathode and electron flow from said cathode is under the influenceof a strong electrostatic field, and said cathode comprising a pair ofmembers spaced in closer proximity to each other than to said anode toproduce a high potential gradient at said cathode with attendant fieldemission of electrons therefrom entirely independent of any gascontinually present in the envelope, and the resulting electrostaticfield causing the evolution of a metal vapor from one of said cathodemembers which forms a metallic arc discharge between said cathodemembers, for initiating a field emission electron discharge accompaniedby enormous current flow between said cathode and anode upon theapplication of a high potential across said cathod members.

6. A field emission are discharge device comprising an envelope, ananode in said envelope, and a cathode disposed adjacent said anode, saidcathode comprising a pair of closely spaced elements for causing an arcdischarge upon the application of a suitable potential across saidelements, and said are discharge forming an electron-emitting source forsupporting a thermionic discharg between said cathode and anodesubstantially independent of any action due to residual gas or vapor insaid device.

7. A field emission arc discharge device comprising an envelope, ananode in said envelope, and a cathode disposed adjacent said anode, saidcathode comprising a pair of closely spaced elements at least one ofsaid elements having a surface of small radii of curvature for causingthe evolution of vaporized metallic particles from on of said elementsand th formation of a metallic arc discharge upon the application of asuitable potential across said elements, and said are discharge formingan electron-emitting source for supporting a thermionic dischargebetween said cathode and anode substantially independent of any actiondue to residual gas or vapor in said device.

8. A field emission arc discharge device comprising an envelope, ananode in said envelope, and a cathode disposed adjacent said anode, saidcathode comprising a pair of closely spaced metallic elements forproducing a high negative gradient at said cathode accompanied by fieldemission of electrons and attendant vaporization of metallic materialwith the formation of a metallic arc discharge upon the application of asuitable potential across said elements, and said metallic arc dischargeforming an electron-emitting source for supporting a thermionicdischarge between said cathode and anode substantially independent ofany action due to residual gas or vapor in said device.

CHARLES M. SLACK. LOUIS F. EHRKE. CLARENCE E. DAWLEY.

